#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<string.h>
int main()
{
	int a;
	int b=1;
	double sum = 0;
	for ( a = 1; a < 101; a++)
	{
		sum += (1.0/a)*b;
		b = -b;
	}
	printf("%f", sum);
	return 0;
}